Nanodragsters hit the street

Rice University scientists have created the ultimate nanovehicle: the nanodragster. The tiny hot rod—1/25,000th the width of a human hair—has a chassis that rotates freely and allows the car to turn when one front wheel or the other is lifted, a behavior not seen in previous nanocars.

RICE—Chemists are building better and better nanomachines, the latest of which is a nanodragster—named for its characteristic hot-rod shape—with small wheels on a short axle in the front and large wheels on a long axle in the back.

The tiny hot rod—1/25,000th the width of a human hair—has a chassis that rotates freely and allows the car to turn when one front wheel or the other is lifted, a behavior not seen in previous nanocars. Images show the nanodragsters appearing to “pop wheelies” with both front wheels raised off the surface.

What those wheels are made of matters most. Early nanocars rolled on simple carbon 60 molecules, aka buckyballs. But they were a drag, literally, as they would only turn on a gold surface in high heat, about 200 degrees Celsius.

The nanodragster design is the latest in a series of molecular machines built by Rice University scientists. Their recent work, reported in the American Chemical Society journal Organic Letters, is another step toward functional nanomachines that can be custom-built and set to work in microelectronics and other applications.

James Tour, the T.T. and W.F. Chao Chair in Chemistry and a professor of mechanical engineering and materials science and of computer science, and his team found in previous research that wheels made of p-carborane, a cluster of carbon and boron atoms, operate at much lower temperatures. But they’re more difficult to image with a scanning tunneling microscope because of their much weaker interaction with metallic surfaces.

The key to making nanodragsters, Tour says, was putting p-carborane wheels in the front and buckyballs in the back, getting the advantages of both. The front wheels roll easier, while the buckyballs grip the gold roadway well enough to be imaged by Kevin Kelly, an associate professor in the Department of Electrical and Computer Engineering. And the vehicle operates at a much lower temperature than previous nanovehicles.

“The trick to making these nanocars was to attach the smaller wheels first, then deactivate their reactive ends through carbon group attachments that we called ‘scythes,’ much like blades on the centers of classical chariot wheels,” Tour says. “Then we could affix the larger C60 wheels to the rear axle.”

Imaging at different temperatures to better understand the energy barriers associated with moving nanovehicles is not discussed in this paper, but the researchers are undertaking such work both on the original gold surfaces and on glass and other substrates. Obtaining greater control of their motion is also the subject of ongoing research.